1. Field of the Invention
The present invention relates to a novel image forming method and more particularly to a method for forming images in which a magnetic developer is imagewise transferred onto a transfer material so as to form an image composed of the developer on the transfer material.
2. Description of the Prior Art
It is well known in the art to obtain an image by uniformly applying a developer (which is referred to also as toner) on a supporting surface and then selectively removing the developer. According to one of known processes to carry out this image forming method there is used a photoconductive toner. The photoconductive toner is uniformly dispersed on a surface, corona charging is carried out on the toner layer and then an imagewise exposure is conducted to selectively erase the electric charge. The photoconductive toner in the selected area is removed to form a desired image. This process is particularly suitable for forming images on a body having a large surface area. However, this process involves some disadvantages. The removed photoconductive toner can not be used repeatedly. A limitation is put on the number of repeating uses of the removed toner. Another problem is that practically useful toner having sufficient photoconductivity to carry out the method is difficult to manufacture.
To solve the above problems, we, the applicant of the present application have already proposed a novel image forming process which is the subject of Japanese patent application laid open No. 60,528/1976. According to the process proposed by the prior application insulating toner is used. The insulating toner is applied uniformly on a support member and then an ion stream is imagewise applied to the toner through ion stream controlling elements such as a photosensitive screen. The toner having charges imagewise modulated by the ion stream is transferred onto a recording material to obtain a desired image.
This prior process has advantages over the aforementioned process employing photoconductive toner. Since, in this process, a simple insulating toner is used as developer, the removed and recovered toner can be used repeatedly almost an infinite number of times. At the same time, the image developing step conventionally required for a common electrophotographic process is no longer necessary in this process. Therefore, high quality images can be obtained in a more stable manner and at a higher speed. Although the process has these remarkable advantages, it has been found that the process still involves some problems. When an imagewise ion stream is applied to the toner support member, a portion of the toner is undesirably stuck on the ion stream controlling element. This is one problem. Another problem concerns the toner application step on the support member. While the process makes the conventional developing step unnecessary, it involves a step of coating the support member with a thin layer of toner as the first step of the process. This coating of toner may be carried out employing any suitable method. However, according to the type of coating method then used, means for applying toner on the support member is required to have almost the same level of function as that required for conventional developing means.